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Onan 5500 run issues

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  • #16
    Originally posted by familytruckster4 View Post

    There are several discrepancies from the Youtube video and whats actually in the Cummins/Onan manual.on page 3-3
    Nowhere does it describe the scenario of running it 30 mins and waiting 6-7 hrs. It also says to fill the oil to the full mark, not what the Youtuber says. And oh BTW, oil does not "expand"
    He also states that 15w40 is only for diesels when the graph on 1-5 shows that 15w40 actually offers the widest temperature range of service. Most modern 15w40 oils such as Mobil Delvac 1300 or Shell Rotella also carry the ratings for use in spark ignited engine (gasoline or LP)
    Like so many other cases of Youtubers its big on advice from a guy thats just another RV owner, I prefer the manuals.

    Also note that page 1-4 shows the fuel must be minimum 87 octane, indicating that it will run on 87. I would however be diligent about not using some of the "super88" octane thats out there right now since this contains 15% ethanol and the vast majority of small engines are not designed for anything more than 10%
    Thanks for the education. Anything that is hot will expand. Think of your radiator expansion tank as an example. Youtube is a great resource but to your point its not always perfect. The point I wanted to make was to check the oil after a short run and soak and with the dip stick screwed all the way in. Since components in the engine are coated with oil where one that sits over winter could show a different level running then letting the unit soak is reasonable. Experience with my dads generac is that oil level and level of the rig is critical on generators. Its always best to read the owners manual if one is available.

    I also completely agree in running Rec fuel unless the generator is used often. I run Rec fuel in my generator as well.

    Last edited by MidwestCamper; 06-22-2022, 06:30 PM.
    2017 Imagine 2600RB
    2015 GMC Sierra 4x4


    • #17
      Originally posted by RoyB View Post
      I am not sure what octane the Onan is designed to run at. I have been putting 91 in this weekend (highest avail). It's 100 degrees out and I am working it hard running the AC all day. I like to run higher octane in extreme heat to reduce any chance of detonation. It's not that out of level. about 1/4 degree both ways.

      The generator ran for a good 12 hours yesterday. It shut down right before I Got back last night since it was still cool inside. It was about 1/4 tank. I went and threw another 5 gallons in and it ran all night without a problem. Put another 5 in this morning. It seems to be using about a .8-1 gal an hour with the AC running all day. I set the temp a little warmer today. Probably don't need to keep it at 72 when I am not in it. The good news is the system will maintain 72 off the generator in 100 degree full sunlight. I think it cycles between the 3 of them so the generator isn't overloaded.

      I will change the plug and filter when I get back. Also keep a spare filter on board as well. I appreciate he help everyone!
      RoyB Running an octane that is higher than recommended will drive more heat since the effective ignition timing will be retarded. Premium fuel will result in later ignition phasing than regular which most likely your generator is made to run on. Just my 2 cents. There may also be an altitude adjustment knob on that unit. But it seems your leveling the rig has made a positive change. Premium has no more fuel system cleaning properties than low octane fuel.

      2017 Imagine 2600RB
      2015 GMC Sierra 4x4


      • #18
        MidwestCamper Jim, I personally have had decent luck with running 1-2 tanks of higher octane fuel just to break up or soften some of the deposits in the bowl faster. Regular fuel will do the same thing, just takes longer.

        Sounds like the OP's generator is getting better. Probably needed to be ran and have the fuel in the cell cycled out.

        I suggest some form of stabilizer in the tank and if you can find it ethanol free fuel. Ethanol fuels can separate out, which leads to running issues, it also absorbs moisture.
        Vehicle: 2018 GMC K2500 Denali Diesel
        Coach: 303RLS Delivered March 5, 2021
        South of Houston Texas


        • #19
          An advantage to running premium fuel is that it usually has less (or sometimes no) ethanol. I used to run premium in my boat (two engines and a generator) for this purpose. I learned the hard way that fuel with ethanol, even with ethanol stabilizer, would foul the carburetors . . . and I had 7 of them to clean (three per engine and one for the generator).

          You can research online for which brands of fuel in your area have ethanol free (usually) premium fuel.

          Cate & Rob
          (with Border Collies Molly & Angel)
          2015 Reflection 303RLS
          2022 F350 Diesel CC SB SRW Lariat
          Bayham, Ontario, Canada


          • #20
            Typical premium in MI has the same amount of ethanol as regular (for now 10%) around here they refer to ethanol free fuel as "rec fuel" and it is 89 octane and usually at least $1 more per gallon than regular. I know some of the verbiage changes regionally. On our trip to Iowa last year I noticed "super 88" fuel at the pumps with little explanation as to what it was. I eventually determined that it was 15% ethanol. I thought it was very poorly defined on the pumps. The ironic part was that in the heart of corn country their ethanol free fuel was only about 45 cents a gallon more than 87 regular.
            Seems like fueling is a learning experience these days
            Last edited by familytruckster4; 06-23-2022, 06:55 AM.
            2021 Reflection 337RLS, 2021 Silverado 3500HD 6.6 gas. Nellie the wonder boxer


            • #21

              All fuels here in the US for road usage is E10. Marine fuel here are either E0 or treated to prevent phase separation and corrosion in the marine environment. Recreation fuel here is typically 89 to 93 octane and is also primarily used here for the marine market or for those that have items such as Stihl saws that need E0 or older equipment that is not compatible with Ethanol. There is no leaded fuel here.
              We have a fuels lab at GM where I had witnessed testing of fuels years ago many times. We would purchase special lab grade fuels at extremely high prices to keep the fuel as consistent as possible. We also had what is referred to as high DI (distillation index) fuel to calibrate engines on less than desirable fuels that could cause startability issues. So a few things from these folks have been shared over the years on fuel.

              Calibration on both premium as well as to a lower octane fuel in order to achieve engine protection on fuels that could induce knock was a daily practice on performance cars. The verbiage can be tricky between premium recommended or premium required. This verbiage has two completely different meanings. Same as regular recommended.

              Running premium in an engine calibrated solely to regular fuel is a waste of money. Some engines can learn the knock system on higher octane fuels to advance the ignition timing. These engines will be described in the owners manual with verbiage that increased performance can be had on higher octane fuels and so on. A generator will not have these expensive feature where the manual will state which fuel to use. Most likely this is regular 87 grade. There could also be verbiage that the generator is 87 minimum. All this means is to never use fuels below 87 octane. Higher grade will actually produce less torque in these engines due to late combustion phasing form a slower burn rate of premium fuel. It will produce more heat, but generally premium will not do any harm so the minimum phrase is used where fuels below the minimum recommendation could create engine damage.

              All fuels contain additives to clean the fuel system where some may be marketed by a variety of catch phrases to make folks think the premium fuel has that extra cleaning capability. It does not.

              If you want to talk engines and powertrains and stay off topic, send me a PM and we can have an endless discussion on fuels, engines and powertrains. Its been my life for decades.

              2017 Imagine 2600RB
              2015 GMC Sierra 4x4